Apparatus for detection of toxic gases, especially carbon monoxide



SES, 2,561,802

c. W. KLUG July 24 1951 APPARATUS FOR DETECTION oF ToxIc GA ESPECIALLY CARBON MoNoxIDE Filed July 15, 194e Patented July 24, 1951 APPARATUS FonvnETEorrIoN oF" TOXIC GASES, ESPECIALLY CARBON MoNoXInE Charles W. Klug,

Chicago, Ill., assigner `to Stewart-Warner Corporation, Chicago,Ill., a corporation ofVirginia i ,Application July 15, 1948Serial N0.f3,8, 816

`4 Claims. (CIJ 23-255) 1 l Thepresent invention -toxic .gasespand especially Acarbon Imonoxide in .theheatedair supplied .tothe-interior of an air ,plane from a` heater ,of the exhaust gas type.

relates Ito `improvements ,innmethods and `a.ppa-ratus for the` detection of This `amcxlicationds acontinuation-in-part of the `prior application, Serial No. 481,426, led Y April 1, 194.3,.now abandoned.

In the copending ,application of` Willard I-I.

vlarr,` WilliamF. Fagen and 4Stanley Kolanowski, ,1

,application Serial No. 478,324, iiled March, 6, '1943, .since abandoned `and the copending continuation- .in-part application, based thereon, Serial No. .54,802, filed .October ,15, 1948,- noW. Patent No.

12,653,179, there is described and claimed 4photo- `sensitive .apparatus .forfdetecting the .presence of toxic ,gases, particularlycarbon monoxide. This @apparatus involvesthe .use `of a substance having fa., photocharacteristic that .changes in, the `pres- ,ence of carbon monoxide. .In its. preferredform .v

`:the apparatus includes, a pair of .glass tubes, in `.which-the substance is ,placed and through `one `ofwhichfreshairis,passed .andis.,used as a v;standard,.and through. the other of which the air `ico-be tested for7 the. `presence of. earbonqnonoxide v .,is. passed. yAssociated with the-tubesis a pair. `of photosensitive` devices., connected l, ,in a balanced V-tliferential vcircuit .insuch manner that when caribon rnonox-ideis present-.fthe circuitis unbalanced =and a suitable controler signal-device is operated. l

. Thesubstance whichis sensitive tothe presence off carbon .monoxide.isonelrnovvn as` the Na- .tional Bureauv of Standards oolorimetric carbon ,monoxide .indicating gel. The `chemical `descrip,- tion and 4method .of ,makingthisgelare fully dis- .closed .in anrarticlennder the title of Rapid Determination `of y Small.v Amounts Lof `Carbon Mon- ;oxide (Preliminary f ReportV .on the NBS Colori- .metric ,indicating Gell by ,Martin Shepherd. ,This articleappearedain ,"Industrial and Engineering Chemistry. (Analytical Chemistry) volume..19,page `77, February11947. This gellis yel- .lowaincolormuntil exposed to carbon,,rnonoxide .Whenfits colorchanges from yellow` progressively towardaa'dark .blue-green. Thus, in theapparatus of the previously mentioned application, if .carbon monoxide is present -in the air to be tested, the .substance inone` of` the .two Vglass tubes .changes-,progressively from a yellovvto` a,.dark

.blue-green color, `thereby `decreasing the .amount sof .light impinging upon `the .photosensitive device associated with, .that tube. As already indicated, vvthis `results :in the Aimbalance `of a, bridge `circu1t, sand the unbalance Aisutilized :to Yoperate. a signal ,orcontrolled device.

It has beenfound in `practice thatvt'he `substance, whichis very sensitive, has atendencyto change color because of the `presence of` very slight concentrations, .of .carbon A,monoxide an'd perhaps other `gases-having atendency todiscolorit. Effortshave been made to overcome u ,this tendency lto discolor by contacting the material with ozone. ",Ihenzone `may be passeddn y.contact with the substance during thedetection of carbon monoxide so that the warning signal or controlled device is 4operated only Awhen, carbon monoxide is presentin concentrations abovea predetermined value. Ozone may `also ``be, passed in contact with the sensitive substance to maintain it in a condition to indicatethe presence Aof carbon ,monoxideor to restore tto acarbon monoxide indicating conditionafter it has been spent .in the indicationnf carbon monoxide. Various methods and ,apparatusior'the aforementioned purposes. areidisclosed and claimedin the `copending application of Willard 41-1. Earr, William F. Fagenandlrank A. Fanta, Jr., Serial ,No. 479,710, ledMarch 19,1943, now abandoned,

and the` copending `continnation-in-part application based thereon, Serial No. 59,702, iiled November l2, 1948.

Aprimaryobjectof the present inventionV is to provide Vimproved methods` and apparatus' `for restoring the carbonmonoxide sensitive substance to a` carbon monoxide indicating condition after its color hasY been changed as a result of being exposedv to carbon `rnorlOXide. 4

Another primary objectof` the present. inventionresides in the provision of vnevv and improved methods Vand apparatus for maintaining .the sensitive substance in a ,carbon monoxide indicating condition, whereby` it may` be .utilized to indicate carbonmonoxde `in concentrations above a certain value.

A further primary object of thelpresent inventionresides in the provision of new and improved .methods of 'andapparatus for detectingthe presbyheating the vmixture to `a temperature above that atwhich ozone is capable of existing. In

other Words, in the practice `of my invention I heat thesensitive substance and expose ittojhe restorative action ofthe loxides of nitrogen-and preferably to oxides of nitrogen obtained in a certain manner.

In the practice of my invention I have produced the oxides of nitrogen by spark discharge in air-an operation I believe produces all the oxides of nitrogen. At the present time I am not certain which of the oxides of nitrogen are the most benecial in so far as the restorative action is concerned, but it does appear that none of the oxides of nitrogen is harmful. In any event, when the oxides of nitrogen are produced as indicated and the ozone removed from the mixture of air, ozone and oxides of nitrogen, and the resulting mixture passed by the'heated sensitive substance, the latter is restored to its original sensitive condition if it has previously been spent, or maintained in condition to indicate carbon monoxide concentrations above a value determined by the concentration of the oxides and the ulength of time that it is exposed thereto.

, It is therefore a further object of the present invention to provide a method of restoring the yA further object of the present invention resides inthe provision of new and approved apparatus for carrying out the methods` of the invention. i jOther objects and advantages of the present ,inventionwill become apparent from the ensuing description, in the course of which reference is Vlhad tothe accompanying drawing, in which:

Fig..1 is a diagrammatic representation of one embodiment of the present invention; s l Fig.' 2 is a view similar to Fig. 1, of a second embodiment of the invention; and

f Fig.3 is a view similar to the rst two iigures of Aa third embodiment of the invention, which embodiment is, in many respects, similar to that of Before considering the details of the physical construction of and the electrical circuits em- ",bodied in the apparatus of the invention, it may `,be well to consider these generally. In brief, the

apparatus of the present invention utilizes a single photosensitive device upon which impinges flight from a single light source, between which yand the deviceis located a transparent tube containing the sensitive substance and through which the light passes. This sensitive substance,

as already indicated, possesses a photocharacteristie-preferably the light transmitting characteristic-which changes in response to the pres- Sence of the substance to be tested, which in this case is taken to be carbon monoxide. The air to be tested is passed through the tube, and should ythis air contain carbon monoxide, the color of ,thesensitive ksubstance changes from yellow progressively to blue-green. As a result less light is transmitted through the sensitive substance to the; photosensitive device. The device is preferablyi arranged to control the now of current through an electron tube in such manner that a warning device or some other controlled device in theoutput circuit of the tube, is operated in response to a predetermined change in the color of the sensitive substance.

Infthe-.embodiment of the invention illustrated in Fig. 1, air from within the airplane cabin, or

4 from the hot air outlet duct of a heater, is continuously passed through a tube containing the sensitive indicating gel. The airplane cabin and heater have not been shown, as these maybe of any conventional construction and do not form any part of the, present invention. The air iiow past the indicating gel may be obtained in any suitable way, as by a vacuum pump or otherwise.

The colorimetric indicating gel is preferably located Within the central portion of a transparent glass tube indicated by the reference character Ill. The indicating gel is shown by the reference character I2, and it occupies the central portion of the tube. Adjacent the opposite ends of the indicating gel are portions i4 of silica gel, and the opposite ends of the tube are iilled with some ilow restricting material, such as glass wool I6, which serves primarily to keep the indicating gel and silica gel within the tube.

In the instant case it is assumed that air from within the interior of the cabin is conducted past the indicating gel. The air ows through a conduit 26 having disposed therein drying material which may include a portion 22 of calcium chlo'- ride and a portion 24 of silica gel. From the dryer the air iiows through a spark discharge apparatus 26 utilized to produce the nitrogen oxides, and thence through a conduit 28 to the tube l0.

' The air iiowing past the indicating gel is substantially continuously although periodically supplied with oxides of nitrogen by the spark discharge apparatus 26. The apparatus includes' a pair of spark electrodes 30 connected to the secondary winding 32 of a transformer 34 through a resistor 36. The primary winding 38 of the vtransformer is connected across the power supply lines 40 and 42 through an adjustable Atiming device 43 arranged periodically to energize the primary of the transformer winding to produce periodic sparks within the nitrogen oxide gener'- ating apparatus. The particular constructioncf the timing device 43 is not material. It maybe of the thermal type, the motor operated cam type, or the electronic type. In one apparatus that I have used, the number of sparks hasbeen per minute, and in this case the timing apparatus was of the motor operated cam type.

In accordance with another of the features of the present invention, any ozone that is generated by the spark discharge apparatus is removed by heating the mixture of ozone, nitrogen oxides, and air generated by the spark discharge apparatus to a temperature above that at which ozone is capable of existing. The heat may be supplied in any suitable manner, as by a resistance type heater 44 permanently connected across the power lines 40 and 42 and located in proximity to the conduit 28 at a point between the spark discharge apparatus 26 and the tube I0'. In practice I have utilized various temperatures to remove ozone, such, for instance, as about C. '.I'his temperature is considerably above the tempera-l ture at which ozone cannot exist, but I preferfto use a higher temperature than actually necessary in order to make certain that no ozone can contact the indicating gel. n s.

The heated air and oxides of nitrogen are vthen cooled before they come into contact with the indicating gel. In the illustrated embodiment there is no positive cooling means provided other than the length of the conduit 28. In the usual installation the length of the conduit between the heater and the indicating tube is sucientto procloser range of :fromtaboutfSOPftoa559f C Thisfis 10..l

doneeby;;the;heat generated ibmthe `light source. egwhiclr unayrzbe flocatedfiwithin:someesuitable t housing; @as` f: diagrammatically findicatedi by;` the dotted lines 150 If desired, the lampijand photo sensitiveideviceemayibe housedwithin azstruoture t 16 alonggthe Alines ofth-atdisclosedi andrclaimedainn thea' aforernentioned,` copending .iapplioatioznl of Ferret'.` alneriai No.14785324;:1ediMa11clr v(if-1943; However, if the heat generated byfthe,larnpand..`

devicewffis 'seither'.toowgreat ortooesmallwthen 2041` thermostaticallycontrolledtemperature chang-` ingeapparatusi ,-may fbe utilized to L maintain.,- thee indicating i gel ewitl'iin..- the, desired: .temperaturen range.;s;.

It' has already :been-indicatedithat.thetempera- 25s ture: at=:which= therindicat-ing ggel lis maintained is -v Preferablywin thefrangefbetween- 'about 45 to 609 i G.; and :particularly ,in the,lregionbetween=-50t and. i 5 thetemperatureuoffthe indicating` gel4 sensitized@` 'when :contactedr-by-r; the: mixtureofl lair f andanitrogeni oxides; Intl-ie temperature per; mitted z to rg0: too high, i thenE thererisrdanger Ithat i the sensitive indicatinggel `will bei destroyed' entirely'by the excessive-,heating'.i` g

'I'heichangednthe amount of* light transmitted-.r thtonghthe findicatingygel i fromffthei lamp to ithe photosensitive dei/ice.` is sY utilized; Ito `control.; ,the y conductivity-fofyanvelectron tubesA 52=1control1ingz the flow of current through a2relay=54:. 1 Thefrelay 40% Mmperates =a switch 56, 'controlling-,thee indicating orfiothen yfcontrolledi' deviceVA 5B'- whi'chi may1 beyfor instance, apparatusficontrolling eitherfthef-'opert ation of thezvheater:orraadampervorg valve-con.-n 1

trolling iutheiiiowi` of heatedfair etofthe. interior .of .n 45

the :airplane rcabin. i

'The uphotosensitive` @device 4 8 :iis preferably `a t photoelec-tricrcell.'` It .fisrr connectedw; across @thenj powerwlines .4 01 and x4 2 throughfza f relatively .Thighs` resistance: resistorY a 6 l-' and; Ether-junction of:l :the 5o :i1

resistorffandiccathodefoff'the cel-l ist; connected tof the grid B2 of the electron tube.

The electron/:tube 521:.isi ibiasedeso i: ,that fit is normally conductive, andi it fis 'so arrangedtrel'aeaselssvli'ght limpinges upon. the cell; zlessffcurrent` ows 'through the tube;` -until iat some predeter# mined f value determined 'by' the initial bias; i ther relay-"Meis yreleased.l They bias for the electron tube `is suppliedfbya biasjresistor y{i4-connected 601i acrossl the power supply llines 'through a bleeder resistor 66 end to the cathode., 68. of the 'tube' through ,annadjustable connectionfl. By. ad-A justing .the connectionli it islpossiblegto .vary the 6@ initial l, grid bias i of the.. tubeand`- thereby... the.` change in color in the indicating, gel. required Ito releaselrelayf 54.1

Thefrelay y54-is-connected lvacross-the. anode-,12

ofethe :electron tube -and'the positive power; sup,- i 70 ply :line '40e/a Ther controlled i ,device'; 58i=is .i coni nectedrbyzconductorl 'l lil toy supply line 421,; andv .byz conductore'l 6 stof-.a txedrcontact associated with switch? 56?; and then-latterfisx connected by-conduce e tonflltothefsupplyline425i* Amaini power] switch i Wi Bof-is providedzfto controlthesupply;fofcizlowers.toeI the apparatus heretofore.described.`

Thesapparatus fis utilized. for the detect-ion; :of carbon,A monoxideein concentrationsew above-e ac; centainifvalue. f The-.concentration;;ofi nitrogen-4` oxides` andT thetimeof operation. oiV the oxide lgen eratorfare adjustedisonthat the oxidesf.override.L or.: counteract-the-e`ect ofcarbon tmonoxiderin. concentrations below-that to -beindicated. In other `:words` when'. thecarbon monoxide conoen.-` tration is ,below the predetermined value-there.- is no: suchE change i inthe color vof the,indicatingigel4 as w-i-ll ldecrease.- .thetow `of current through they. electron tube :and relay toa point where ,the lrelay iis.released.y Ontheother hand-whenthe conm.

centration :of carbon lmonoxide .reaches `the g pre1A determined; value,- then,` the. flow of? currentf. through the relayuis decreased toa 4p oir1t-iwhere.a` it.iisireleasedandthe switch` 56 closes thencrollt through. controlled device 58 Toplace theapparatus inoperatiomthe switchlf` (ifiisclosed. thereby .to energize the .various cuitsn. The-lampAB `is energized .and it generates. heat to maintainitheindicating geliatia tempera-w ture betweenabout 50fnanda55- C. The heater. Mds valsoenergized .and it raises thetemperaturel of-the mixture of air, ozone, .and '.oxidesf nitrogen to a temperature of about 150 CLto remove alLtraces ofozone.; Atthe sametimeVthe spark.-discharge apparatus is, periodically `placed into operationunderthe control `ofthe timeror .i periodic circuit closer 43.

Under normal-` conditions, thatis, Uwhen itherei isf no leakage.. inthe .heat exchangerfand.. no car-..

plane cabin, the air flowing past the indicating .i gel containstno considerable amountfarbon. monoxide... In any` event, the carbon monoxide which may, .be presentk due to., other .causesr such;I u for, instance, `as smokingonleakage from the `eX-A haust .of .otherengines or the` likeVis `ins,u-hcientA to produce,anynoticeable ,color change in .theine dicating gel. because of. the i overriding 'eiiect of. thebxidesof nitrogen.. The` air is caused to ow past,theindicatinggel through thechemical dry: ers 22 .,and,'24,` andpast the electric spark producingapnaratus 26 andthe heater 44.

`When `the carbonF monoxide contenter theair, reachesthe `desiredpredetermined value. .atfwhich i the relay isto be operatedthenthecarbon mon-V oxide efe`cts.a suiiicient changeincolor ofjthe. gel to decrease.the'conductivitymof the electron, tube 52to a point at which the .relay .54 is-.released and` switch., ,5d is closed. `to operate the. controlled device 58.'r I

Once operated to indicate the presence of car-` bon monoxide, the, device 58 remainspperated until theair within the interior of lthe .cabin is4 cleared-'of .carbon. monoxideV to a concentration." less than the predetermined concentrationand.. the `relayll fiper'ated.` Once .the zconcentrationf has been so decreased, the nitrogen oxides restore the indic'ating'gel 'to its original colorand con-`` i ditionywithpth result 'thatfthe electron tube 52j.'

is 4rendered more Aconductive andjthe vrelav54` is;

energized suiliciently to operate switch 56'.

Itinay benoted, thereforefthat' inthe normal. operation-oi the embodiment of the` invention ofL Fig: 1, thre'edistihct'methods are-involved= The rst of ltlieseis the primary methodofi'detection" offth'epresence-of-fthe gas; the-second isthe maintenance of the indicating gelin conditionfto' indicate-the presenceiof the gas and thrthird.`- isithe `restoration 'ofthe indicating 'gel intoarconf dition 1toi--iindicate the pres'encefof-i'carbon. mom-a1A afee-1,802@

a vconcentration equal to or above the predeterniined concentration. In addition, there is included in'this embodiment of theinvention, means for maintaiing the apparatus out of operation as long as the plane is on the ground. a

Referring now to Fig. 2 (in which elements corresponding to those shown in Fig. 1 are indicated by like reference characters), it may be noted that the conduit 20 through which air from withinthe interior of the cabin is supplied to the apparatus is'normally closed by `a valve |00 operable by a solenoid |02. In addition, it will be Inoted that the power switch 80 is normally opened, 'but Vin this case is operable by a relayv When'theplane is on the ground the solenoid |02 and relay |04 are both ie-energized, therebyA preventing the ow of air from within the cabin past the indicating gel and disconnecting the apparatus from the source of power. When the airplane leaves the ground the solenoid and relay are energized by ,a switch |06 operable at a desired altitude by an air pressure responsive sealed bellows |00. When the switch |06 is closed, the solenoid and relay are connected in parallel across the power lines 40 and 42 by a circuit including conductors and H2 connected to the power lines 40 and 42, respectively." Thus, when the plane is off the ground, the'k valve |00 is opened to permit ow of air through the apparatus, and the switch 80 is closed to energi'ze the electrical portion of the apparatus.

The nitrogen oxide generating apparatus 26 is normally Vinoperative and its operation is controlled conjointly by a timer ||4 and a relay 6 inthel plate circuit of the electron tube 52. The relay ||6`is normally operated and is adapted to be released when the current flow therethrough and through the electron tube decreases to a value indicative of a concentration of carbon monoxide below the predeterminedA concentration at which the warning signal or controlled device 50 is to be operated.

lWhen the concentration of carbon monoxide reaches this lower critical value, then the relay ||6 releases its associated switch ||8 and the latterconditions the oxide generating equipment for operation by the timer ||4. The closure of the switch connects the timer and primary wind` ing 33 of the transformer across the power lines through conductors |20, |22, and |24, leading to switch I I0 and conductor |26.

Inthe instant embodiment of the invention,l

the timer is of a character adapted to place the oxide generating apparatus into operation for a certain denite time interval and to keep it out of operation for another time interval. For instance, these time intervals may be one minute on and three minutes oil`, i. e., during the on period sparking occurs across the electrodes 30,:,as by interruption of the transformer priv.

mary circuit. The nitrogen' oxide generatingY equipment is thus placed into operation for` adenite time interval and then kept out of operation for another definite time interval. result 'isthat if the carbon monoxide concentration causing release of relay I6 is not above the i predetermined value at which the controlled def vice 58 is to be operated, then the time of opera'- within the cabin is cleared of carbon monoxide',`

after which the relay ||6 is again operatedV to open switch ||8.

In the event the concentration of ther change in color of the indicating gel. This further change in color of the indicating gel decreases furtherl the ilow of current through 'the electron tube,- with theresult that a second relay |30, also in the plate circuitof tube 52, releases its associated switch |32, to connect the controlled device 58 across the power lines '40 and 42. Thus,

the nitrogen oxide generating equipment is placed'- into operation when carbon monoxide is present in concentrations less than the predetermined'- concentration (which concentration maybev a known toxic concentration),- and thereafter remains in operation, and if the vconcentration of f carbon monoxide issuch as'to overcome the restorative effect of the nitrogen oxides, then the Warning signal is operatedf The embodiment of Fig. `:l is similar to that` of Fig.- 2, except in yso faras" the relay arrange'-r mentis concerned. Here the relay |50 is con` stituted by a pair of opposed portions |52 and |54, only the former of which is in-the plate circuit of the electron tube 52. 'I'heportion |54 is connected across the y-power lines 40 and `42 through a resistorl |56 adjusted so that at normal condition, i. e., when there'is'no carbon monoxide present, the current now through` relay section. |54 is equal to the currentwow through'ref lay |52.

Under normalconditions,y the two coil sections oppose 'each other with equal forces so that a. pair of switches |58 and |60 associated with the relay are normally open. The switches'aresobiased by springs |64 that as `the flow of current through the electron tube and portion |52 of the relay decreases in response to discoloration of the indicatinggel, the switch |58 is first closed by theforce4 exerted -thereon by relay portion I|54 and then upon a further decrease in current the switch |60 is closed. Closure of switch |58y places= the nitrogen oxide generatingapparatus 26 into operation, as described above in conjunction with Fig.` 2, while closure of switch |60 operatesthe' controlled device 58.

l1t is'beiieved that further disclosure 'of the operation ofthe embodiment of Fig. 3 is unnecessary, except thatit might be pointed out'that here again the oxide vgenerating equipment is placed into operation when carbon monoxide is present at a critical concentration belowfthe predetermined or toxic concentration, .and `that `it,

remains in operation, untilthe vcarbon: monoxide The Y carbonmonoxide within the cabin increases to the predetermined value at' which the controlled device is to be operated,l then the restorative eiTect Voi? the nitrogen oxides is insuilicient to prevent 'fur-" concentration falls, but is maintained in operation should the carbon monoxide concentration rise to the predetermined concentration at which the controlled device is operated.

The methods of restoring and maintaining the indicating gel in condition to indicate may be practiced apart from the method of detection. For instance, tubes containing the sensitive substance may be maintained in condition to be ready to indicate the presence of carbon monoxide by maintaining them in a heated condition and exposing them to the oxides of nitrogen. The tubes may likewise be utilized for visual observation of the presence of carbon monoxide and after they have been spent by indication of carbon monoxide, they may be returned to their original condition. This return or restoration may be effected by heating the tubes and exposing the gel to the action of the nitrogen oxides in the manner heretofore described. After being thus restored, the tubes may be transported and used wherever desired for the purpose of providing visual indication of the presence of carbon monoxide.

From the foregoing detailed description of the present invention, it should be noted that its principles may be applied in various ways. It should be understood, therefore, that the details of the various embodiments are not intended to be limitative of the invention except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

l.. An apparatus for detecting the presence of a gas constituent in a gaseous medium by the use of a substance in gas permeable form, which undergoes a photocharacteristic change in the presence of said constituent, said apparatus coniprising: a light transmitting container constructed to support said substance for passage of gas therethrough, a conduit connected to said container for conducting the medium to be tested to said container, a restoring gas generator in said conduit to generate a restoring gas when energized, a lamp and a photoelectric cell arranged to receive light from the lamp through the container, and means operated by said photoelectric cell for energizing said generator when the light received by said cell drops to a predetermined level and a controlled device operated by said photoelectric cell when the light received by said photoelectric cell drops to a second predetermined level lower than the iirst said level.

2. An apparatus for detecting the `presence of a gas constituent in a gaseous medium by the use of a substance in gas permeable form, which undergoes a photocharacteristic change in the presence of said constituent, said apparatus comprising: a light transmitting container constructed to support said substance for passage of gas therethrough, a conduit connected t-o said container for conducting the medium to be tested to said container, a restoring gas generator in said conduit to generate a restoring gas when energized, a lamp and a photoelectric cell arranged to receive light from the lamp through the container, and means operated by said photoelectric cell for energizing said `generator when the light received by said cell drops to a predetermined level.

3. An apparatus for detecting the presence of a gas constituent in a gaseous medium by the use of a substance in gas permeable form, which undergoes a photocharacteristic change in the presence of said constituent, said apparatus comprising: a light transmitting container constructed to support said substance for passage of gas therethrough, a conduit connected to said container for conducting the medium to be tested to said container, electrodes for producing an electric spark in said conduit when said electrodes are energized, a heater for heating the gas passing through said conduit at a point between said electrodes and said container, a lamp and a photoelectric cell arranged to receive light from the lamp through the container, and means operated by said photoelectric cell for energizing said electrodes when the light received by said cell drops to a predetermined level and a controlled device operated by said photoelectric cell when the light received by said photoelectric cell drops to a second predetermined level lower than the first said level.

4. An apparatus for detecting the presence lof a gas constituent in a gaseous medium by the use of a substance in gas permeable form, which undergoes a photocharacteristic change in the lpresence of said constituent, said apparatus comprising: a light transmitting container constructed to support said substance for passage of gas therethrough, a conduit connected to said container for conducting the medium to be tested to said container, electrodes for producing an electric spark in said conduit when said electrodes are energized, a heater for heating the gas passing through said conduit at a point between said electrodes and said container, a lamp and a photoelectric cell arranged to receive light from the lamp through the container, and means operated by said photoelectric cell for energizing said electrodes when the light received byv said cell drops to a predetermined level.

CHARLES W. KLUG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,919,858 Pettingill June 25, 1933 2,019,871 Pettingill et al. Nov. i5, 1935 2,111,301 Schroter Mar. 15, 1938 2,114,383 Jacobson Apr. 19, 1938 2,234,499 McAllister Mar. 11, 1941 2,295,366 Stout Sept. 18, 1942 2,349,963 Harrison May 30, 1944 

2. AN APPARATUS FOR DETECTING THE PRESENCE OF A GAS CONSTITUENT IN A GASEOUS MEDIUM BY THE USE OF A SUBSTANCE IN GAS PERMEABLE FORM, WHICH UNDERGOES A PHOTOCHARACTERISTIC CHANGE IN THE PRESENCE OF SAID CONSTITUENT, SAID APPARATUS COMPRISING: A LIGHT TRANSMITTING CONTAINER CONSTRUCTED TO SUPPORT SAID SUBSTANCE FOR PASSAGE OF GAS THERETHROUGH, A CONDUIT CONNECTED TO SAID CONTAINER FOR CONDUCTING THE MEDIUM TO BE TESTED TO SAID CONTAINER, A RESTORING GAS GENERATOR IN SAID CONDUIT TO GENERATE A RESTORING GAS WHEN ENERGIZED, A LAMP AND A PHOTOELECTRIC CELL ARRANGED TO RECEIVE LIGHT FROM THE LAMP THROUGH THE CONTAINER, AND MEANS OPERATED BY SAID PHOTOELECTRIC CELL FOR ENERGIZING SAID GENERATOR WHEN THE LIGHT RECEIVED BY SAID CELL DROPS TO A PREDETERMINED LEVEL. 